Copper is a widely used industrial material generally produced by melting a copper charge, casting the melted charge into a convenient intermediate form, and then either hot or cold working (or a combination of hot and cold working) the intermediate form into the desired product. Modern copper rod production facilities operate in a continuous fashion, with the speed of the rod at the end of the process being in the range of at least about 500 feet per minute (about 150 meters per minute). Copper is a chemically active material which tarnishes at room temperature and oxidizes more significantly at elevated temperatures. Thus, if hot working techniques are used to produce the copper product, and such techniques are performed in a oxidizing environment, oxides will form on the surface of the product, which must eventually be removed. It is known to remove such oxides mechanically by, for example abrasion or machining, or to remove such oxides in an acid bath, commonly referred to as pickling. Is also known that oxides can be removed by long time exposure to a gaseous reducing atmosphere, or by exposure to an aqueous alcohol solution.
A variety of gases have been suggested to reduce copper oxide. These include hydrogen and the various reducing gases produced by incomplete combustion of fuel. In general, cleaning of oxidized copper surfaces by treatment in a gaseous reducing atmosphere is performed in a batch type operation which can last several hours.
The removal of oxides from copper surfaces in a continuous process has been suggested by Snyder et al in U.S. Pat. No. 3,562,025; to avoid embrittling the copper rod, Snyder states that hydrogen should not be used in such a process. Snyder describes the use of a multi-step process, wherein the wire is first heated to a temperature below about 1,000.degree. F. (about 540.degree. C.) and is then inductively heated in a reducing atmosphere chamber to a temperature between about 1,100.degree. and 1,400.degree. F. (between about 595.degree. and 760.degree. C.) Related U.S. Pat. Nos. 3,546,029 and 3,659,830 also to Snyder relate to the gaseous cleaning of oxidized copper rod using reducing gases generated by incomplete combustion. These patents specify residence times of about one-half to five minutes in the reducing atmosphere, with rod velocities on the order of about three to twelve inches per minute (about 7.5 to 30 centimeters per minute). Such slow rod velocities are not practical in a state-of-the-art copper rod production facility.
Accordingly, there remains a need for a process to remove oxide layers from hot rolled copper rod on a continuous basis and at a velocity of more than 500 feet per minute (about 150 meters per minute).